1. Field of the Invention
The present invention relates to a portable lighting device, and in particular to a portable lighting device, which utilizes absorption and release of light energy by a light storing agent and can be used for lighting in dark place or at nighttime.
2. Description of the Prior Art
In the past, various types of portable lighting device have been developed and used in practical application. In general, a portable lighting device as described above comprises a battery, a miniature electric lamp, a cylindrical casing, a switch, a reflection plate (or dish), a transparent sealing material, etc. In the conventional type portable lighting device as described above, the switch is turned on, and light is emitted from the miniature lamp and lighting is provided only during the period when electric power is connected to the miniature lamp. Some of the conventional type portable lighting devices contain a light storing material so that, even after the power is turned off by switch, light energy absorbed and stored by the light storing material is released, thus providing lighting to the surroundings. A portable lighting device utilizing the light storing material is disclosed in U.S. Pat. No. 4,546,416 (Pemberton). In this U.S. patent, a bezel or a rim around a lens, used as a sealing material and arranged in front of the miniature lamp, is made of semi-transparent synthetic resin, and a light storing material is added when the synthetic resin is molded.
Consequently, the ring-like bezel absorbs light from the miniature lamp, and even after the miniature lamp is turned off, light is emitted from the bezel and provides lighting to the surroundings.
However, there is limitation to the volume of the ring-like bezel because of its shape and function, and hence, there is also limitation to total amount of the light storing material. For this reason, after the switch is turned off on the portable lighting device, the time of light emission from the light storing material is very short.
In the conventional portable lighting device, considerable degree of illuminance can be obtained when switch is turned on and light is emitted from the miniature lamp. However, when performing work in a dark room or, for example, when observing constellations of stars at night and it is wanted to see astronomical table or other material in the dark, the light with high illuminance is too dazzling and blinding to the user because pupils of human eyes are widely opened in the dark. When exposed to the light too dazzling, the pupils are extremely closed down. As a result, after switch is turned off on the portable lighting device, some time is required until the user becomes familiar with the dark place again. During this period, the user cannot, see anything around in the dark.